2,039 research outputs found
Extending the scope of microscopic solvability: Combination of the Kruskal-Segur method with Zauderer decomposition
Successful applications of the Kruskal-Segur approach to interfacial pattern
formation have remained limited due to the necessity of an integral formulation
of the problem. This excludes nonlinear bulk equations, rendering convection
intractable. Combining the method with Zauderer's asymptotic decomposition
scheme, we are able to strongly extend its scope of applicability and solve
selection problems based on free boundary formulations in terms of partial
differential equations alone. To demonstrate the technique, we give the first
analytic solution of the problem of velocity selection for dendritic growth in
a forced potential flow.Comment: Submitted to Europhys. Letters, No figures, 5 page
An Uncommon Cause of Acute Bowel Obstruction: The Left Para.Duodenal Hernia
Internal hernias of the abdomen are uncommon. They represent less than 1% of bowel obstruction cases. The left Paraduodenal hernia (PH) is the most frequent type of internal hernias. We report a case of 77 year- old woman consulting for bowel obstruction evolving since two days. The abdominal computed tomography revealed a retroperitoneal small bowel contained in a peritoneal sac. The surgical exploration confirmed the diagnosis of a left internal PH by showing incarcerated jejunal loops in a PH through a narrow opening to the left of the angle of Treitz. A surgical reduction of the hernia and closure of the hernia neck were performed. The follow-ups were uncomplicated. Through this observation and a literature review, we try to recall the clinical and radiological characteristics of this disease and toclarify the therapeutic modalities.Keywords: Computed tomography, internal hernia, paraduodenal hernia, small bowel obstructio
Universality in two-dimensional Kardar-Parisi-Zhang growth
We analyze simulations results of a model proposed for etching of a
crystalline solid and results of other discrete models in the 2+1-dimensional
Kardar-Parisi-Zhang (KPZ) class. In the steady states, the moments W_n of
orders n=2,3,4 of the heights distribution are estimated. Results for the
etching model, the ballistic deposition (BD) model and the
temperature-dependent body-centered restricted solid-on-solid model (BCSOS)
suggest the universality of the absolute value of the skewness S = W_3 /
(W_2)^(3/2) and of the value of the kurtosis Q = W_4 / (W_2)^2 - 3. The sign of
the skewness is the same of the parameter \lambda of the KPZ equation which
represents the process in the continuum limit. The best numerical estimates,
obtained from the etching model, are |S| = 0.26 +- 0.01 and Q = 0.134 +- 0.015.
For this model, the roughness exponent \alpha = 0.383 +- 0.008 is obtained,
accounting for a constant correction term (intrinsic width) in the scaling of
the squared interface width. This value is slightly below previous estimates of
extensive simulations and rules out the proposal of the exact value \alpha=2/5.
The conclusion is supported by results for the ballistic deposition model.
Independent estimates of the dynamical exponent and of the growth exponent are
1.605 <= z <= 1.64 and \beta = 0.229 +- 0.005, respectively, which are
consistent with the relations \alpha + z = 2 and z = \alpha / \beta.Comment: 8 pages, 9 figures, to be published in Phys. Rev.
âChemlali Mhassenâ: New olive cultivar derived from crossbreeding program in Tunisia with high oil quality and productivity
The new olive cultivar âChemlali Mhassenâ was derived from the autopollination of the Tunisian oil cultivar âChemlali Sfaxâ. The main morphological differences between the two cultivars were observed on the endocarp (symmetry, position of maximum diameter, apex, base and surface). On the agronomic plan, this cultivar is distinguishable from the original cultivar due to its medium earliness of bearing (4 years), medium alternate bearing (0.44), early ripening, moderate sensitivity to verticillium and its high olive production per tree (7.7 kg). Concerning oil quality, âChemlali Mhassenâ had higher performances than the original cultivar for oleic acid content (70 to 77 %) and lower contents for palmitic acid (9.2 to 11.5 %) and linoleic acid (9.3 to 14.7 %). Similar performances were recorded between the new and the original cultivars for rhizogenesis behavior and pollen compatibility
Strong-coupling behaviour in discrete Kardar-Parisi-Zhang equations
We present a systematic discretization scheme for the Kardar-Parisi-Zhang
(KPZ) equation, which correctly captures the strong-coupling properties of the
continuum model. In particular we show that the scheme contains no finite-time
singularities in contrast to conventional schemes. The implications of these
results to i) previous numerical integration of the KPZ equation, and ii) the
non-trivial diversity of universality classes for discrete models of `KPZ-type'
are examined. The new scheme makes the strong-coupling physics of the KPZ
equation more transparent than the original continuum version and allows the
possibility of building new continuum models which may be easier to analyse in
the strong-coupling regime.Comment: 21 pages, revtex, 2 figures, submitted to J. Phys.
Surface Instability in Windblown Sand
We investigate the formation of ripples on the surface of windblown sand
based on the one-dimensional model of Nishimori and Ouchi [Phys. Rev. Lett. 71,
197 (1993)], which contains the processes of saltation and grain relaxation. We
carry out a nonlinear analysis to determine the propagation speed of the
restabilized ripple patterns, and the amplitudes and phases of their first,
second, and third harmonics. The agreement between the theory and our numerical
simulations is excellent near the onset of instability. We also determine the
Eckhaus boundary, outside which the steady ripple patterns are unstable.Comment: 23 pages, 8 figure
Early stage scaling in phase ordering kinetics
A global analysis of the scaling behaviour of a system with a scalar order
parameter quenched to zero temperature is obtained by numerical simulation of
the Ginzburg-Landau equation with conserved and non conserved order parameter.
A rich structure emerges, characterized by early and asymptotic scaling
regimes, separated by a crossover. The interplay among different dynamical
behaviours is investigated by varying the parameters of the quench and can be
interpreted as due to the competition of different dynamical fixed points.Comment: 21 pages, latex, 7 figures available upon request from
[email protected]
Universal macroscopic background formation in surface super-roughening
We study a class of super-rough growth models whose structure factor
satisfies the Family-Vicsek scaling. We demonstrate that a macroscopic
background spontaneously develops in the local surface profile, which dominates
the scaling of the local surface width and the height-difference. The shape of
the macroscopic background takes a form of a finite-order polynomial whose
order is decided from the value of the global roughness exponent. Once the
macroscopic background is subtracted, the width of the resulting local surface
profile satisfies the Family-Vicsek scaling. We show that this feature is
universal to all super-rough growth models, and we also discuss the difference
between the macroscopic background formation and the pattern formation in other
models.Comment: 5 pages, LaTex, 1 figure, minor correction
Anomalous Dimension and Spatial Correlations in a Point-Island Model
We examine the island size distribution function and spatial correlation
function of a model for island growth in the submonolayer regime in both 1 and
2 dimensions. In our model the islands do not grow in shape, and a fixed number
of adatoms are added, nucleate, and are trapped at islands as they diffuse.
We study the cases of various critical island sizes for nucleation as a
function of initial coverage. We found anomalous scaling of the island size
distribution for large . Using scaling, random walk theory, a version of
mean-field theory we obtain a closed form for the spatial correlation function.
Our analytic results are verified by Monte Carlo simulations
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